The present invention relates to mixing apparatus in general, and more particularly to improvements in gravity operated mixing apparatus which can be utilized for intimate mixing of ingredients of pharmaceutical or chemical products.
It is often necessary to produce a mixture of two or more flowable materials preparatory to the making of pills, tablets, granulae and/or analogous pharmaceutical or chemical products. Certain types of flowable materials must be treated in such a way that they are subjected to minimal or negligible wear in the course of the mixing operation. As a rule, such materials should be intensively intermixed within a short interval of time and should form a mixture which is sufficiently homogeneous for immediate conversion into pills, tablets and the like.
Some flowable materials which are used for the making of pills and like chemical and/or pharmaceutical products are of highly toxic nature. Therefore, it is desirable and advantageous to avoid renewed transfer of such toxic materials from vessel to vessel because each transfer can entail the escape of some toxic materials with attendant contamination of the surrounding area and potential injury to the attendants.
Certain presently known mixing apparatus for flowable materials which are to be converted into pills, tablets or like pharmaceutical or chemical products constitute so-called positive or compulsory mixers wherein one or more rotary mixing or stirring elements are driven by one or more motors. The vessel which confines the flowable materials to be intermixed is held at a standstill. An advantage of such positive mixers is that the mixing operation is intensive and can be completed within very short intervals of time. However, such mixers exhibit the drawback that the rapidly rotating stirring or mixing elements are likely to cause a pronounced rubbing action between the particles of the materials to be mixed as well as between such particles and the rotating mixing elements. Moreover, when the mixing of a charge is completed, the resulting product must be transferred from the mixing vessel into a transporting receptacle. By the same token, a fresh charge must be admitted into the mixing vessel from one or more discrete receptacles. All this consumes time and enables certain harmful or potentially harmful ingredients to escape during admission into and/or during evacuation from the mixing vessel.
It is further known to mix two or more flowable materials in so-called gravity operated mixers wherein the mixing vessel is caused to move up and down while rotating about a vertical axis. Such mode of mixing is less likely to subject the particles of flowable materials to extensive wear but the period of mixing is relatively long and the intensity of the mixing action is often unsatisfactory.